1. Field of Invention
This invention relates to a conveyor mechanism of the walking beam type.
More specifically, the invention relates to a compact, low cost, general purpose walking beam conveyor for automatically transferring work pieces in a straight-line path from a pick-up station to a discharge station where they can be used in a manufacturing assembly operation, or the like. The walking beam conveyor according to the invention is designed to employ conventional, commercially available components, a minimum number of mechanical linkages, low friction moving parts of proper design and so interconnected that build-up of internal conflicting binding and frictional forces are avoided or minimized, and minimum size drive components are used for a given size design load range by employing conter-balancing spring developed forces which assist the load bearing members.
2. Background Problem
Walking beam conveyors have been used for the purpose of automatic work piece transfer in the field of automated assembly line manufacturing processes for a number of years. Some of the known walking beam conveyor designs are disclosed in the following U.S. Pat. Nos.: 1,883,763--issued Oct. 18, 1932; 3,089,687--issued May 14, 1963; 3,215,260--issued Nov. 2, 1965; 3,481,450--issued Dec. 2, 1969; and 3,857,479--issued Dec. 31, 1974. From this list of known prior art patents, it will be appreciated that walking beam conveyors have been available to the art for at least fifty years and their use in automated manufacturing facilities is now well established.
Most walking beam conveyors provide a repeated pattern of straight-line movements starting from a neutral or home position which is best described as comprising up-forward-down-back to home position. Half-way through the up movement, the walking beam picks up the work piece or other load to be transferred, moves it forward to a location over the discharge point, deposits the work piece or load at the discharge point half-way through the down movement and then returns back to the home position. The early walking beam conveyor designs, as shown for example in U.S. Pat. No. 1,883,763 and 3,089,687, were made primarily to transfer large and heavy parts such as automobile engine blocks, steel beams and the like. The heavy load and need for accurage location of the load dictated the use of automatic, hydraulic or pneumatic actuators driving through various combinations of mechanical linkages and are complex and costly due to the use of a large number of external control components such as limits, switches, relays, valves, pumps, hydraulic or pneumatic reservoirs, etc. The devices also are relatively slow since one movement must be completed before another can be initiated.
Another category of known walking beam conveyors is exemplified by U.S. Pat. Nos. 3,215,260 and 3,481,450 for use with smaller loads and requires the use of specially designed, multi-groove cams or families of cams mechanically interconnected to provide the desired intermittent up-forward-down-back movement to the walking beam member. These devices, however, require specially designed component drive cams and follower linkages which increase their cost and complexity. U.S. Pat. No. 3,857,479 purportedly describes a less complex and inexpensive walking beam conveyor which employs a motion generating prime mover mechanism that drives an output member around a substantially square path that defines four substantially equal isolated strokes. This design while adequate for light load requirements such as processing candy boxes to be loaded with candy one layer at a time, for example, cannot readily be adapted for use with heavier intermediate weight loads without incurring considerable expense in beefing-up the prime mover mechanism. In order to overcome the deficiencies of the known walking beam conveyor designs and provide an improved, compact, general purpose, low cost walking beam conveyor adaptable for use with intermediate weight loads and the like, the present invention was devised.